Cracked LCD panels aren't the only reason why notebook
screens go dark. If you can't see anything on your notebook screen it may be caused
by one of the following faults too:
1) The backlight isn't working; dead
inverter.
Laptop screens use either Light Emitting Diodes
(LED) or miniature fluorescent light bulbs called Cold Compact
Fluorescent Lights (CCFL) to backlight the panel and make text formed by
the Liquid Crystal Display (LCD) visible. CCFLs are the older
backlight technology of the two and require a separate power
supply called an "inverter" which frequently fails. The inverter
supplies high voltage Alternating Current (AC) to excite a
small amount of Mercury vapour contained in the CCFL bulbs. The excited
mercury vapour emits a strong ultraviolet light which subsequently causes
an internal coating of fluorescent powder to fluoresce and emit a bright
visible white light.
It's pretty cool technology and I highly recommend
you watch 'The Secret Life of Machines'
- Season 3, Episode 4 (Youtube link) by Tim Hunkin for the
best explanation and demonstration of how fluorescent lights work that you will
ever see! The key demo starts at 13m:14s and runs to 16m:00s. (All hail Tim Hunkin for creating the
best television series ever!)
embedded video 480x360 in commented out text
Getting back
to the problem; if there's no functional backlight, you can't see what's on the display. CCFL's do burn
out after a few 10's of thousands of hours continuous use, but tend to go
dim or orange in colour before fizzling entirely. When a notebook screen "just goes dark" it usualy
means the inverter which powers the CCFL's has died.
The inverter is a separate electrical circuit
from the LCD panel, usually nestled in the lower part of the
screen bezel between the hinges. Power from the notebook goes in
one side, two white rubbery high voltage wires come out the opposite and
connect to the CCFL bulb in the LCD panel. Again, if your screen uses
LED backlights none of this applies.
If the inverter circuit fails and
you replace the LCD panel the screen still won't work, you need to replace the inverter circuit board too. For
most laptops, once you have the screen bezel open it's not too difficult to
replace the inverter with a new one and reconnect the wires.
To reiterate - LED backlit notebook screens do not use
an inverter, so this type of failure does not apply to this kind of screen. Most
laptop manufacturers have adopted LED backlights, but if you're searching out
replacement LCD panels you must be certain to get the right
type for your particular notebook as some laptops are made in
both LED and CCFL backlight variants depending on where in the world they
are sold (ie. LED for first world, CCFL for third world markets).
2) Broken or loose video cable.
As with a computer monitor, the screen in your laptop has a
cable connecting it to the rest of the computer over which video data is sent.
Because of the compact nature of notebooks and the hinge, a special
flexible cable is used which can become damaged or in
some situations the connectors can work loose. If that happens, the screen is
essentially unplugged and nothing will show up on the display, Nine times out
of ten, bad design cracks the flat wire harness and you'll need to find a cable and replace it.
This is a challenging prospect, but not impossible and certainly helped if
you can track down a notebook service manual or disassembly video
published to YouTube. In the olden days, if you were handy with a soldering iron it
was possible to fix the cable harness, but with today's pin
densities that's just about impossible.
3) Loose Component
Connections
Big notebooks with separate graphics cards can sometimes experience situations where the
videocard becomes unseated after a jarring drop. This will
usually prevent the whole computer from booting up and you may be lucky
enough to resolve the fault by opening up the rear access panels and reseating the videocard
and memory modules. We had a Dell laptop once that "died" in this manner.
The cheap plastic chassis allowed too much flex so when it
was dropped (in a protective case) it wouldn't boot up again. The fix was to
remove the memory, hard drive and battery and then reinsert them firmly. Worked like a
charm. Never bought a Dell laptop again. :-)
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